| Abstract | U ovoj disertaciji istražena je klasa izravno pogonjenih hidrauličkih sustava upravljanih
dvjema pumpama. Sustav je analiziran s aspekta regulacije položaja, energetske
učinkovitosti te interneta stvari. Predložen je nelinearni dinamički model sustava, gdje su
glavne nelinearnosti trenje u cilindru te protoci kroz proporcionalni ventil. Za regulaciju
sustava predložene su četiri različite metode. Prve dvije metode odnose se na linearne
regulatore, a to su ISA PID i LQR-I regulator. Iz nelinearne teorije upravljanja odabran
je SMC regulator i metoda povratnog koraka.
Za sve predložene upravljačke metode dobiveni su simulacijski rezultati za dvije sinusne
pobude i jednu skokovitu. Dobiveni simulacijski rezultati usporedeni su sa simulacijskim
rezultatima proporcionalnog elektrohidrauličkog sustava te eksperimentalnim rezultatima
za oba sustava. Iz eksperimentalnih rezultata, koji su dobiveni za različita opterečenja,
izračunato je šest parametara pomoču kojih se usporedivala statička i dinamička točnost
sustava. Iz odziva sustava na sinusne pobude izračunate su pogreške u fazi i amplitudi te
kumulativna pogreška sustava, dok je za skokovitu pobudu izračunato vrijeme porasta i
vrijeme smirivanja odziva te kumulativna pogre_ska sustava. Pomoću navedenih parametara
komentirana je statička i dinamička točnost sustava u odnosu na različite regulatore
i klasični elektrohidraulički sustav.
Energetska učinkovitost sustava izračunata je za različita opterečenja sustava i sve
predložene regulatore. Dan je primjer seta mjerenih podataka iz kojih je izračunata
energetska učinkovitost sustava kao omjer izlazne i ulazne energije sustava. Dobiveni
rezultati međusobno su usporedeni za pojedine regulatore i sustave te su pokazali da je
DDH sustav energetski učinkovitiji od klasičnog elektrohidrauličkog sustava.
Sa stanovišta IoT-a predloženo je rješenje za udaljeni nadzor i upravljanje sustavom.
Razvijen je model baze podataka i web aplikacija te su istraženi mrežni industrijski protokoli.
Na kraju, dan je zaključak ovog rada te su predložene smjernice za daljnja istraživanja. |
| Abstract (english) | In this thesis, comprehensive investigation of a class of direct-driven hydraulic (DDH)
systems controlled by two pumps is carried out. The DDH system is investigated from
the standpoints of control theory, energy efficiency, and the Internet of Things (IoT). A
nonlinear dynamical model of the system is proposed, wherein the main nonlinearities
in the proposed model are friction inside the cylinder and ow through the proportional
valve. Four different methods have been proposed for solving of fixed and variable setpoint
(dynamic trajectory) tracking problems. The first two methods are chosen from the linear
control theory, and they are the ISA PID and LQR-I controllers. The SMC controller and
backstepping control were chosen from the nonlinear control theory.
Simulation results were obtained for the step and dual sine wave reference trajectory
for all proposed control methods. Simulation results were compared with ones obtained
for proportional electrohydraulic systems, and with experimental results for both systems.
Six parameters were calculated from obtained experimental results for different cylinder
payloads. Based on these six parameters, the static and dynamic accuracy of the system is
evaluated and compared. From the results obtained for the sine wave reference trajectory,
phase, amplitude, and cumulative control system error were calculated. The rise and settling
time together with cumulative system error were calculated from system response to
stepwise reference (setpoint) change. With given parameters, steady-state and dynamical
accuracy of the system is evaluated for different control methods and compared to the
classical electrohydraulic system.
The energy efficiency of the proposed system was calculated for different cylinder
payloads and proposed control methods. Energy efficiency has been calculated as the ratio
of the output and input system energy based on a measured data set. The obtained results
for proposed control methods are mutually compared for DDH and classical hydraulic
systems. Results showed that the DDH system's energy efficiency is higher in comparison
to the classical electrohydraulic system.
From the aspect of IoT, a solution for remote system monitoring and control has been
proposed. Web application and database model were developed while network-specific
industry protocols have been investigated. Finally, the main contributions of this thesis
have been summarized in the conclusion section, which has also given guidelines for further
research.
This thesis is organized in eight chapters, whose contents are outlined below.
Chapter 1: Introduction. In this chapter, a detailed literature review on the topic
of this thesis is presented. Motivation for this research is given alongside an overview
of the previous work. Based on the detailed literature review, hypotheses and scientific
contributions are defined. The outline of the thesis also provided herein.
Chapter 2: Experimental setup. This chapter describes the experimental setup used
to carry out all the tests presented in this thesis. Hydraulic schematics for proportional
and DDH system are also shown. A detailed description of all used components is given
along with their technical specifications.
Chapter 3: Mathematical modeling. The nonlinear mathematical model of the system
is derived in this chapter. First, the dynamical model of the hydraulic cylinder is
given, incorporating the nonlinear LuGre friction model. Proportional valve dynamics are
modeled as the second-order lag term while the flows through the valve are represented
by a nonlinear static function normalized over the maximum range of the control spool
movement. A proportional term with volumetric efficiency is used for describing the dynamical
behavior of the gear pump. Finally, state-space models of the DDH and classical
hydraulic system are given as fifth-order and seventh-order lag terms respectively.
Chapter 4: Classical control methods. From the linear control theory, two control
methods are chosen for solving of fixed and variable setpoint (dynamic trajectory) tracking
problems. The first control method is widely used the ISA PID controller. The
controller parameters are obtained with the Ziegler-Nichols method. Simulation results
are given for the case of a fully loaded cylinder and comparison has been carried out
between the classical system and DDH system through experimental results. For different
proportional-integral-derivative (PID) controller structures experimental results are
given and mutual comparison between individual PID controller types has been performed.
Linear quadratic regulator (LQR) type state controller with integral action (LQR-I)
is chosen as the alternative linear control method, with parameters for the proposed control
method obtained from a linearized dynamic process model. Obtained experimental
results indicated superior control performance (i.e. faster response and smaller control
error) compared to the PID controller.
Chapter 5: Nonlinear control methods. The sliding mode controller (SMC) and
backstepping state-space controller are selected from the nonlinear control system methods
in order to further improve set point accuracy and trajectory tracking ability. For both
controllers, simulations are carried out and their results compared to those obtained for
the classical system, as well as with experimental results for the fully loaded cylinder.
In particular, the obtained experimental results show excellent response and tracking
capabilities for sine wave reference input. For the case of step reference input signal, both
controllers showed roughly the same transient dynamics and obtained similar results as
ISA PID and LQR-I controllers.
Chapter 6: Energy efficiency. In this chapter, the energy efficiency of the proposed
system is investigated. The equations used for calculating the system power and energy
are defined. For the cylinder velocity estimation, an algebraic approach is used to determine
signal time-derivatives of arbitrary order. An example set of measured data from
which energy efficiency is calculated is given for both the DDH and classical hydraulic
system. Thus obtained results are mutually compared for both systems and different
control methods used in this thesis. Finally, some general conclusion on energy efficiency
have been given.
Chapter 7: Remote system control and monitoring. An Internet of Things (IoT)
solution for remote system control and monitoring is presented in this chapter. Firstly, a
schematic representation of the proposed setup is given. Connections between programmable
logic controller (PLC), human-machine interface (HMI), camera, web server and,
user are defined and explained. A detailed literature review on industrial network protocols
is also given herein. Modbus TCP protocol is chosen, as the most suitable protocol
for communication between PLC and web server. A suitable database model is designed
for continuous data logging and system overall monitoring, with the user administration
database model is adopted from the Web2py framework. The developed web application
is user-friendly and easy to use. It provides for sending the information to the PLC and
monitoring of all relevant data in real-time, with easy integration of new systems being
possible through the system administration page.
Chapter 8: Conclusion. In this chapter main contributions of the dissertation have
been listed, and all hypotheses are confirmed. Several recommendations are given for
future research. |
